Multi-stage interference suppression

ABSTRACT

A multi-stage interference suppression receiver includes a short equalizer section configured to operate on a first portion of a received signal received over a channel to produce a first equalized signal and a first estimate of the channel, a channel estimator section configured to operate on the first equalized signal to produce a second equalized signal, the channel estimator section comprising a linear estimator and a non-linear estimator, a long equalizer section configured to operate on a second portion of the received signal to produce a first estimate of symbols in the received signal and a second estimate of the channel and an interference canceller section configured to operate on the first estimate of symbols in the received signal to generate a second estimate of symbols in the received signal based on, at least in part, the second estimate of the channel.

REFERENCE TO CO-PENDING APPLICATIONS FOR PATENT

The present application for patent is related to co-pending U.S. patentapplication Ser. No. 12/038,724, entitled “COHERENT SINGLE ANTENNAINTERFERENCE CANCELLATION FOR GSM/GPRS/EDGE,” filed Feb. 27, 2008,assigned to the assignee hereof, and expressly incorporated by referenceherein.

The present application for patent is related to co-pending U.S. patentapplication Ser. No. 12/464,311, entitled “TWO DIMENSIONAL SEARCH FORGERAN: OPTIMAL TIMING AND CARRIER RECOVERY,” filed May 12, 2009,assigned to the assignee hereof, and expressly incorporated by referenceherein.

The present application for patent is related to co-pending U.S. patentapplication Ser. No. 12/193,995, entitled “ENHANCED GERAN RECEIVER USINGCHANNEL INPUT BEAMFORMING,” filed Aug. 19, 2008, assigned to theassignee hereof, and expressly incorporated by reference herein.

The present application for patent is related to co-pending U.S. patentapplication Ser. No. 12/478,195, entitled “ITERATIVE INTERFERENCECANCELLATION RECEIVER,” filed Jun. 4, 2009, assigned to the assigneehereof, and expressly incorporated by reference herein.

The present application for patent is related to co-pending U.S. patentapplication Ser. No. 12/553,855, entitled “SYMBOL ESTIMATION METHODS ANDAPPARATUSES,” filed Sep. 3, 2009, assigned to the assignee hereof, andexpressly incorporated by reference herein.

BACKGROUND

1. Field

The present invention relates to wireless communication and, inparticular, relates to interference cancellation at a receiver.

2. Background

In many communication systems utilizing GSM, GPRS, EDGE or the like, areceiver's ability to properly decode a received signal depends upon thereceiver's ability to effectively suppress co-channel interference (CCI)and inter-symbol interference (ISI). As wireless communications becomeever more prevalent, however, increasing amounts of CCI and ISI cannegatively affect a receiver's ability to suppress interference.

SUMMARY

In one aspect, a communication receiver comprising a short equalizersection, a channel estimator section, a long equalizer section and aninterference canceller section is disclosed. The short equalizer sectionis configured to operate on a first portion of a received signalreceived over a channel to produce a first equalized signal and a firstestimate of the channel. The channel estimator section configured tooperate on the first equalized signal to produce a second equalizedsignal, the channel estimator section comprising a linear estimator anda non-linear estimator. The long equalizer section is configured tooperate on a second portion of the received signal to produce a firstestimate of symbols in the received signal and a second estimate of thechannel. The interference canceller section is configured to operate onthe first estimate of symbols in the received signal to generate asecond estimate of symbols in the received signal based on, at least inpart, the second estimate of the channel.

In another aspect, a signal reception method is disclosed. The methodcomprises producing a first equalized signal and a first estimate of achannel by operating on a first portion of a received signal receivedover the channel, producing a second equalized signal using the firstequalized signal and one of a linear estimator and a non-linearestimator, estimating a first estimate of symbols in the received signaland a second estimate of the channel from a second portion of thereceived signal, and generating a second estimate of symbols in thereceived signal based on the second estimate of the channel.

In yet another aspect, a machine-readable medium comprising instructionsfor receiving a signal at a receiver is disclosed. The instructionscomprise code for producing a first equalized signal and a firstestimate of a channel by operating on a first portion of a receivedsignal received over the channel, code for producing a second equalizedsignal using the first equalized signal and one of a linear estimatorand a non-linear estimator, code for estimating a first estimate ofsymbols in the received signal and a second estimate of the channel froma second portion of the received signal, and code for generating asecond estimate of symbols in the received signal based on the secondestimate of the channel.

In yet another aspect, a signal reception apparatus comprising means forproducing a first equalized signal and a first estimate of a channel byoperating on a first portion of a received signal received over thechannel, means for producing a second equalized signal using the firstequalized signal and one of a linear estimator and a non-linearestimator, means for estimating a first estimate of symbols in thereceived signal and a second estimate of the channel from a secondportion of the received signal, and means for generating a secondestimate of symbols in the received signal based on the second estimateof the channel is disclosed.

In yet another aspect, a communication device comprising a memory and aprocessor is disclosed. The processor is configured to executeinstructions to produce a first equalized signal and a first estimate ofa channel by operating on a first portion of a received signal receivedover the channel, produce a second equalized signal using the firstequalized signal and one of a linear estimator and a non-linearestimator, estimate a first estimate of symbols in the received signaland a second estimate of the channel from a second portion of thereceived signal, and generate a second estimate of symbols in thereceived signal based on the second estimate of the channel.

It is understood that other configurations of the subject technologywill become readily apparent to those skilled in the art from thefollowing detailed description, wherein various configurations of thesubject technology are shown and described by way of illustration. Aswill be realized, the subject technology is capable of other anddifferent configurations and its several details are capable ofmodification in various other respects, all without departing from thescope of the subject technology. Accordingly, the drawings and detaileddescription are to be regarded as illustrative in nature and not asrestrictive.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates an exemplary communication system in accordance withcertain configurations of the present disclosure;

FIG. 2 is illustrates exemplary frame and burst formats in a GSMtransmission, in accordance with certain configurations of the presentdisclosure;

FIG. 3 is a block diagram of a portion of a receiver, in accordance withcertain configurations of the present disclosure;

FIG. 4 is a block diagram of a short equalizer section, in accordancewith certain configurations of the present disclosure;

FIG. 5 is a block diagram of a channel estimator section, in accordancewith certain configurations of the present disclosure;

FIG. 6 is a flow chart of an exemplary decoding process, in accordancewith certain configurations of the present disclosure;

FIG. 7 a is a block diagram illustrating a receiver in accordance withcertain configurations of the present disclosure;

FIG. 7 b is a block diagram illustrating a receiver in accordance withcertain other configurations of the present disclosure;

FIG. 8 is a chart illustrating frame error rate performance improvementsachievable utilizing certain aspects of the subject technology, inaccordance with certain configurations of the present disclosure;

FIG. 9 is a chart illustrating symbol error rate performanceimprovements achievable utilizing certain aspects of the subjecttechnology, in accordance with certain configurations of the presentdisclosure;

FIG. 10 is a block diagram illustrating an apparatus with which certainaspects of the subject technology may be implemented in accordance withcertain configurations of the present disclosure;

FIG. 11 is a block diagram illustrating an apparatus with which certainaspects of the subject technology may be implemented in accordance withcertain configurations of the present disclosure; and

FIG. 12 is a block diagram illustrating a computer system with whichcertain aspects of the subject technology may be implemented inaccordance with certain configurations of the present disclosure.

DETAILED DESCRIPTION

Receivers operating in accordance with certain wireless standards, suchas GERAN, often receive signals over a channel that may be characterizedas a fading channel. Operation of a receiver often involves receiving asignal, extracting symbols from the received signal and demodulating thesymbols to produce data bits. To help produce the data bits accurately,a receiver may also suppress (or remove) signal distortions caused bythe communication channel, noise, interference from unwantedtransmitters, and so on. Receivers are often designed by makingassumptions about communication channels (e.g., assuming that acommunication channel has a finite impulse response of a certainduration) and noise signal (e.g., assuming that noise has a whitespectrum). Based on the assumptions made, a practitioner of the art mayconfigure a receiver to suppress the signal distortions by performingchannel equalization using, for example, maximum likelihood (ML)detection, decision feedback equalization (DFE), minimum least squaresestimate (MLSE) and other well-known algorithms. While algorithms suchas the MLSE may provide optimal results in many applications, MLSE tendsto be computationally expensive, making it an unattractive option forimplementation at a resource-limited wireless device. Furthermore,computational complexity of the MLSE algorithm increases non-linearlywith increasing constellation density of the received signals.Therefore, in communications network that use higher order modulationschemes (e.g., 8PSK), a channel equalization and/or an interferencesuppression technique that is computationally less expensive than MLSEis desirable.

Channel equalization techniques using MLSE are generally called“non-linear” channel equalization techniques in the art. Othertechniques such as channel equalization using a liner combiner aregenerally called “linear” channel equalization techniques. Broadlyspeaking, MLSE algorithm works better than other techniques when someinformation is available about a channel and/or received signalamplitude distortion is severe. In certain aspects, configurations ofthe present disclosure provide methods and systems wherein channelequalization and interference suppression may be performed using eithera non-linear technique such as MLSE or a linear technique such as alinear combiner, based on certain operational conditions of thereceiver. These operational conditions include, for example,constellation density of the received signal and severity of distortionin the received signal. In one aspect, such architecture is advantageousfor a receiver expected to receive signals with different modulationschemes in the same network. For example, the GERAN Evolution standarduses modulation schemes including GMSK, QPSK, 8PSK, 16-QAM and 32-QAM.

Broadly and generally speaking, in certain aspects, the presentdisclosure provides signal reception techniques wherein a receiver isoperationally optimal in the sense of minimizing probability of error.In one aspect, a receiver suppresses interference blindly. In anotheraspect, a receiver uses signal processing techniques having relativelylow complexity. In another aspect, a receiver is robust to frequencydifferential between a desired signal and interference. In certainaspects, the present disclosure provides signal reception techniquesapplicable to a multi-input multi-output (MIMO) channel. In certainconfiguration, a MIMO channel is characterized by having multiplereceive antennas at a receiver configured to receive signals frommultiple transmit antennas at a transmitter.

The following abbreviations are used throughout the disclosure.

-   CCI=co-channel interference-   EDGE=enhanced data rate for GSM evolution-   eSAIC=enhanced single antenna interference cancellation-   FER=frame error rate-   GERAN=GSM EDGE radio access network-   GP=guard period-   GSM=Global Standard for Mobile communication (Groupe Mobil Special)-   IC=interference cancellation/canceller-   ISI=inter-symbol interference-   LLR=log-likelihood ratio-   MDD=minimum distance detector-   MEQ=multiple stream equalizer-   MIMO=Multiple input multiple output-   ML=maximum likelihood-   MLSE=maximum likelihood sequence estimator-   MMSE=minimum mean squared error-   MSIC=multiple stream inter-symbol interference cancellation-   PHIC=parallel hierarchical interference cancellation-   PSK=phase shift keying-   RLS=recursive least squares-   RSSE=Reduced state sequence estimation-   SER=symbol error rate-   SNR=signal to noise ratio-   TDMA=time domain multiple access

FIG. 1 illustrates a communication system 100 in accordance with oneaspect of the subject technology. The communication system 100 may, forexample, be a wireless communication system based on the GSM standard. Areceiver 102 receives a signal 104 transmitted by a base station 106 atan antenna 108 coupled to the receiver 102. However, as illustrated, thesignal 104 may suffer from impediments such as co-channel interference(CCI), including a transmission 110 from another base station 112, andinter-symbol interference (ISI) comprising one or more reflections 114of the signal 104. Accordingly, in certain aspects, the receiver 102processes the signal 104 to suppress effects of CCI and ISI and recoverthe data transmitted by the base station 106 by estimating receivedsymbols. While FIG. 1 depicts a single antenna 108 for the sake ofclarity, it is contemplated that configurations of the presentdisclosure also include MIMO transmission systems and the receiver 102may have multiple receive antennas to receive the signal 104.

FIG. 2 shows exemplary frame and burst formats in GSM. The timeline fordownlink transmission is divided into multiframes. For traffic channelsused to send user-specific data, each multiframe, such as exemplarymultiframe 202, includes 26 TDMA frames, which are labeled as TDMAframes 0 through 25. The traffic channels are sent in TDMA frames 0through 11 and TDMA frames 13 through 24 of each multiframe, asidentified by the letter “T” in FIG. 2. A control channel, identified bythe letter “C,” is sent in TDMA frame 12. No data is sent in the idleTDMA frame 25 (identified by the letter “I”), which is used by thewireless devices to make measurements for neighbor base stations.

Each TDMA frame, such as exemplary TDMA frame 204, is furtherpartitioned into eight time slots, which are labeled as time slots 0through 7. Each active wireless device/user is assigned one time slotindex for the duration of a call. User-specific data for each wirelessdevice is sent in the time slot assigned to that wireless device and inTDMA frames used for the traffic channels.

The transmission in each time slot is called a “burst” in GSM. Eachburst, such as exemplary burst 206, includes two tail fields, two datafields, a training sequence (or midamble) field, and a guard period(GP). The number of bits in each field is shown inside the parentheses.GSM defines eight different training sequences that may be sent in thetraining sequence field. Each training sequence, such as midamble 208,contains 26 bits and is defined such that the first five bits arerepeated and the second five bits are also repeated. Each trainingsequence is also defined such that the correlation of that sequence witha 16-bit truncated version of that sequence is equal to (a) sixteen fora time shift of zero, (b) zero for time shifts of ±1, ±2, ±3, ±4, and±5, and (3) a zero or non-zero value for all other time shifts.

FIG. 3 is a block diagram of a receiver 300, in accordance with certainaspects of the present disclosure. The receiver 300 comprises a shortequalizer section 302, a channel estimator section 304, a long equalizersection 306, interference canceller section 308, a de-interleaversection 310 and a channel decoder section 312.

The short equalizer section 302 is configured to generate a firstequalized signal 322 (e.g., a first set of equalized symbols) bycanceling CCI and ISI from a first portion of the received signal (e.g.,a midamble or a preamble). The short equalizer section 302 alsogenerates a first estimate of the channel (e.g., impulse responsecoefficients) on which the received burst of symbols was received. Theshort equalizer section 302 uses, for example, a blind channelestimation algorithm to obtain the first estimate of the channel andcalculate a first set of equalized symbols. The short equalizer section302 may initially operate upon a received signal corresponding to ashort input sequence comprising a known signal (e.g., midamble) anditeratively process additional received signal samples, as furtherdescribed below.

The channel estimator section 304 is configured to use the firstestimate of the channel and the first equalized signal (input 322) tofurther estimate channel and further suppress ISI from the first set ofequalized symbols and output a second equalized signal (output 324).

A long equalizer section 306 uses the second equalized signal 324 tofurther equalize the channel and suppress ISI and produce a firstestimate of symbols in the received set of symbol (output 326). The longequalizer section 306 also produces a second estimate of the channelusing the second equalized signal (also included in output 326).

An interference canceller section 308 uses the second estimate of thechannel and the first estimate of symbols (collectively output 326) torefine the results to improve symbol decisions. The interferencecanceller section 308 produces hard symbol decisions and log-likelihoodvalues associated with the symbol decisions (together shown as output328). The symbols values from the output 328 are used by furtherreceiver sections such as a de-interleaver 310 to generate data samples330, which are further decoded by a channel decoder 312 to producedemodulated data 332.

FIG. 4 is a block diagram illustrating the operation of a shortequalizer section 302, in accordance with certain configurations of thepresent disclosure. As depicted in FIG. 4, the optimal timing section402 provides timing information 403 to the short equalizer section 302.Furthermore, the optimal frequency section 404 provides an estimate 405of a carrier in the received signal to the short equalizer section 302.In certain configurations, the optimal frequency section 404 computes anoptimal estimate 405 by evaluating an SNR value, as further described indetails below. The short equalizer section 302 uses the optimal timinginformation 403 to minimize estimation error incurred during channelequalization calculations. For example, the timing information 403 isuseful in deciding the start time and the duration of a time windowcomprising the first portion of the received signal (e.g., midamble).The short equalizer section 302 uses the frequency estimates 405 forrecovering a carrier in the received signal. An optimal frequencyestimate 405 helps improve performance of channel equalization byminimizing the estimation error. The short equalizer section 302 thusproduces a first equalized signal output Y1 408 (substantially identicalto output 322 of FIG. 3) from a set of input samples X 406, receivedfrom an earlier receiver section such as analog-to-digital converter(not shown in FIG. 4) and a set of symbols of known values S_(TSC) 410(e.g., a preamble or a midamble).

Still referring to FIG. 4, in certain configurations, the optimal timingand the optimal frequency calculations are performed sequentially. Forexample, first, an optimal timing estimate 403 is obtained by minimizinga target function (e.g., minimizing least squares error), by holdingfrequency offset to a constant value. Next, frequency estimate 405 isimproved by holding the optimal timing estimate unchanged andcalculating another target function (e.g., SNR) by changing thefrequency offset. This process is iteratively repeated until no furtherimprovements are achieved or until expiration of a time allocated forthe calculation. For example, the SNR calculations is performed bychanging frequency offset by one or more of {−200, −100, −50, 0, +50,+100, +200} Hz. One example error function for finding optimal timing isto minimize estimation error of a known set of symbols in the receivedsignals. For example, in a GSM network, when the short equalizer 302operates upon midamble section of the received signal, midambleestimation error is used as the error criterion for minimization duringoptimal timing estimation. In certain configurations, maximizing SNR isused as the error criterion for finding optimal frequency estimates 405.

The above-described optimal timing and optimal frequency recoverytechniques are merely exemplary and several other optimizationtechniques well known in the art are possible. For example, previouslyreferenced U.S. Patent Application No. 61/052,973 titled “TWODIMENSIONAL SEARCH FOR GERAN: OPTIMAL TIMING AND CARRIER RECOVERY,”incorporated herein by reference in its entirety, discloses variousmethods of timing and carrier recovery.

FIG. 5 is a block diagram of the channel estimator section, inaccordance with certain configurations of the present disclosure. Thechannel estimator section 304 receives an estimate of symbols Y1 408from a previous signal processing section (e.g. the short equalizersection 302). The channel estimator section also receives an estimate H₁510 of the channel (e.g., from the short equalizer section 302). Incertain configurations, the channel estimator section 304 is configuredto use output of one of either an MLSE channel 506 (output 512) or alinear combiner (briefly called a combiner) 504 (output 514) to outputequalized symbols. The multiplexer 508 selects either all the equalizedsymbols from the output 512 or all the equalized symbols from the output514 to produce the equalized symbols S_(equ) at the output 324. Incertain configuration, only one of the MLSE section 506 and the combinersection 504 is operated on a given received signal. In certain otherconfigurations, both the MLSE sections 506 and the combiner section 504are operated simultaneously, and an appropriate output is selected bythe multiplexer 508 to convey to the output 324.

The choice of operation of the MLSE section 506 and/or the combinersection 504 can be made in a variety of ways. For example, in certainconfigurations, the choice is fixed a priori, based on the modulation ofsignals received during operation of the receiver 102. For example, incertain configurations, MLSE section 506 is used only when the inputsignal comprises GMSK modulation and the input symbols have two possiblevalues (e.g., 1-bit per symbol encoding), and the combiner section 504is used when other (higher) constellation densities are received. Incertain other configurations, the choice between sections 504 and 506 ismade at run time. When calculations performed during channel estimation(e.g., at section) show that the received signal suffers from severeamplitude distortion, then MLSE section 506 is used, otherwise combinersection 504 is used. Such a run-time selection advantageously allows thereceiver 102 to allocate computational resources to receive signals onan “as needed” basis, freeing up the computational resources for othertasks at the receiver 102.

The output 324 is used by the long equalizer section 306. In certainconfigurations, the operational principles of the long equalizer section306 are similar to the operational principles of the short equalizersection 302 discussed before. The long equalizer section 306 computes aset of channel equalized output samples 326 using the equalized symbolset S_(equ) 324 as the training sequence and the input samples X 406. Incertain configurations, the long equalizer section 306 operates upon atraining sequence having a larger number of samples compared to theshort equalizer section 302. For example, in a GSM network, the longequalizer section 306 is operated on 142 samples, comprising 116 datasamples and 26 midamble samples.

The interference canceller section 308 shown in FIG. 3 produces anoutput 328 comprising symbol decisions and log-likelihood values for thesymbol decisions. Previously referenced co-pending U.S. patentapplication Ser. No. 12/553,855, titled “SYMBOL ESTIMATION METHODS ANDAPPARATUSES”, incorporated herein by reference in its entirety,discloses certain configurations of operation of the interferencecanceller section 308 consistent with certain configurations of thepresent disclosure.

To describe certain configurations comprising various sections depictedin FIG. 3 in mathematical terms, the received signal samples of signaland interference (noise) can be written as below. For example, given aset of spatial and temporal samples at a time k:

$\begin{matrix}{{{\underset{\_}{x}}_{k} = \begin{bmatrix}{x_{k}(1)} \\{x_{k}(2)} \\\vdots \\{x_{k}(M)}\end{bmatrix}},\mspace{14mu}{{\underset{\_}{s}}_{k} = \begin{bmatrix}s_{k} \\s_{k - 1} \\\vdots \\s_{k - \upsilon}\end{bmatrix}}} & \left( {1a} \right)\end{matrix}$

where s_(k) is the midamble/quasi-midamble signal at time k, s _(k) is a(υ+1)×1 midamble/quasi-midamble vector, and x _(k) is a M×1 receivedmidamble/quasi-midamble vector, a set of spatial temporal samples can bedefined as

$\begin{matrix}{{X_{k} = \begin{bmatrix}{\underset{\_}{x}}_{k} \\{\underset{\_}{x}}_{k - 1} \\\vdots \\{\underset{\_}{x}}_{k - L}\end{bmatrix}},} & {\left( {1b} \right),}\end{matrix}$

where X_(k) is a M×(L+1)×1 vector of spatial temporal samples with aspatial length of M and a temporal length L+1, where M is the number ofMIMO receive antennas on the receiver 102, L is the temporal stackingfactor used to temporally stack received samples, ν is channel memoryand P is the length of the midamble or quasi-midamble that representsthe length of the burst signal being used in a given iteration, andwherein each of M, L, ν and P is a positive integer. The received signalsamples can then be written as a function of convolution of the receivedsymbols through a linear filter and an additive noise term as:x ₁(k)=h ₁ ^(T) s(k)+g ₁ ^(T) z(k)+n ₁ , x ₂(k)=h ₂ ^(T) s(k)+g ₂ ^(T)z(k)+n ₂,  (1c)

The task performed in the linear combiner 504 of the channel estimatorsection 304 can then be expressed as follows: estimate s _(k) given x_(k). Previously referenced U.S. application Ser. No. 12/038,724, titled“COHERENT SINGLE ANTENNA INTERFERENCE CANCELLATION FORGSM/GPRS/EDGE,”incorporated herein by reference in its entirety,discloses various techniques that may be utilized to perform suchestimation.

In certain configurations, more samples are used for calculating resultsof channel equalization using MMSE, so that a full column rank formatrix inversion is obtained. In such configurations, the input signalsamples are spatially and temporally stacked to obtain the followingmatrix:X _(k) =[x ^(T)(k), x ^(T)(k−1) . . . x ^(T)(k−L)]^(T)  (2)

Accordingly, a spatial/temporal structured matrix can be constructed,such that[X]=[X _(k) , X _(k+1) , . . . , X _(k+P−υ)],  (3)

where [X] is a M (L+1)×(P−υ) matrix. As an example, in a GSM network,P=26. Similar to the data matrix [X], temporal/spatial stacking for thesymbols in the received signal gives the symbol matrix in equation (4).[S]=[S _(k) , S _(k+1) , . . . , S _(s+P−υ)],(υ+1)×(P−υ)  (4)

As is well-known in the art, an interference suppression filter that cansuppress interference can be expresses as:W=[S][X] ^(T) {[X][X] ^(T)}⁻¹,(ν+1)×M(L+1)  (5)

Using the expression in equation (5) above, the output Y1 408 of theshort equalizer section 302 shown in FIGS. 3 and 4 can be written as:Y1=[W][X],(ν+1)×(P−ν)  (6)

In certain configurations, the number of midamble samples used toestimate output Y1 408 may be increased from one iteration to the next,during the iterative process of channel equalization. For example, incertain configurations when the received signal is a GSM signal, thechannel equalization calculations can start with using P=26,corresponding to the number of samples of midamble 208. In eachsubsequent iteration, more and more data bits can be included as thechannel estimate improves. For example, in certain configurations, oneadditional sample from each side of the midamble 208 may be added to thesymbol matrix [S] shown in equation (4).

Certain aspects of the channel estimator section 304 can be explained inmathematical terms as follows. The output of the short equalizer section302 can be expressed in terms of an equivalent channelY1=[H]₁[S],  (7)

In equation (7), [H]₁ is the equivalent channel estimate, with dimension(ν+1, ν+1) and [S] is the (ν+1, P−ν) reference symbol matrix shown inequation (4). Generally speaking, output Y1 408 of the short equalizer302 is a vector of streams of symbol values that has cancelled asignificant amount of CCI, but a relatively smaller amount of ISI fromthe input signal X 406. The least-squares (LS) estimate of [H]₁ is asshown in equation (8) below. The channel estimator section 304calculates the LS estimate[Ĥ]₁=[Z][S]^(H)[SS^(H)]⁻¹.  (8)

As previously discussed, in certain configurations, the channelestimator section 304 calculates the LS estimate [Ĥ]₁ using either anon-linear or a linear algorithm, decided either at run time or apriori. Certain aspects of the linear algorithm, implemented at thecombiner 504, can be explained in mathematical terms as follows.

The output Y1 408 of the short equalizer 302, as described above, canalso be represented as a matrix shown in equation (9) of estimatedsymbols to further explain the working of the combiner 504.

$\begin{matrix}{\left\lbrack {Y\; 1} \right\rbrack = \begin{bmatrix}{\hat{s}}_{v}^{0} & {\hat{s}}_{v + 1}^{0} & {\hat{s}}_{v + 1}^{0} & {\hat{s}}_{v + 1}^{0} & \cdots & {\hat{s}}_{N - 1}^{0} \\{\hat{s}}_{v - 1}^{1} & {\hat{s}}_{v}^{1} & {\hat{s}}_{v + 1}^{1} & {\hat{s}}_{v + 2}^{1} & \cdots & {\hat{s}}_{N - 2}^{1} \\\vdots & \vdots & \vdots & \vdots & \vdots & \vdots \\{\hat{s}}_{0}^{v} & {\hat{s}}_{1}^{v} & \cdots & {\hat{s}}_{v}^{v} & \cdots & {\hat{s}}_{N - 1 - v}^{v}\end{bmatrix}} & (9)\end{matrix}$

It can be seen that the [Y1] matrix in equation (9) has a Toeplitz-likeappearance, with an estimate symbol appearing in a row below, shiftedone column to the right. For example, when the short equalizer 302 hasequalized the channel to a large extent, the symbol ŝ_(ν) ⁰ in the firstrow and first column has approximately the same value as the symbolŝ_(ν) ¹ in the second row, second column, and so on. In certainconfigurations, when using the short equalizer 302 for equalizing GSMsignals, the matrix [Y1] has dimension 5 rows×138 columns, correspondingto a 4-tap filter for channel equalization and using received signalsamples comprising 116 data bits and 26 midamble symbols.

In the combiner 504 of FIG. 5, the symbol estimates are calculated as aweighted combination of the diagonal terms of [Y1] (terms that will besubstantially identical to each other, due to the Toeplitz-structure, asexplained above). For example, a linear combination of a symbol estimatecan be expressed as:

$\begin{matrix}{{{{\hat{s}}_{c}(k)} = {\frac{1}{v + 1}{\sum\limits_{i = 0}^{v}{{\hat{s}}_{k}^{i}\alpha_{i}}}}},\mspace{14mu}{v \leq k \leq {N - 1 - {v.}}}} & \left( {10a} \right)\end{matrix}$

In equation (10a) above, N represents the maximum burst length of thesignal. For example, in a GSM network, N=138 (corresponding to 116 datasamples plus 26 midamble samples minus 4, channel memory filter delay).The weighting factors are given as

$\begin{matrix}{{\alpha_{i} = {\sum\limits_{j = 0}^{v}{{\hat{H}}_{i,j}}^{2}}},\mspace{14mu}{0 \leq i \leq v}} & \left( {10b} \right)\end{matrix}$

It can be seen from equations (10a) and (10b) that symbol estimates areexpressed as a linear combination of (ν+1) previously estimated symbols.For example, in a GSM network, the value ν may be chosen to be equal to5. In such a network, a linear combination of 6 symbols is used toobtain a symbol estimate expressed in equation (10). The weightingfactors given in equation (10b) estimate the energy in the impulseresponse of the estimated filter for each channel. Therefore, theweighting factors weigh the effect of each symbol in equation (10a) inproportion of the energy in the corresponding channel.

The output estimates obtained by solving equation (10a) are thenhard-sliced to obtain hard estimates of symbols (first estimate ofsymbols), and provided as output 328 to the interference canceller 308.

The interference canceller section 308 is configured to operate on thefirst estimate of symbols from output 326 to generate a second estimateof symbols in the received signal based on, at least in part, a secondestimate of the channel.

FIG. 6 is a flow chart of an exemplary decoding process 600, inaccordance with certain configurations of the present disclosure. Thedecoding process 600 produces demodulated data samples from an inputsignal received over a channel. In certain configurations, the decodingprocess 600 is implemented at a receiver 102. The decoding process 600comprises the operation 602 of producing a first equalized signal and afirst estimate of the channel by operating on a first portion of areceived signal received over a channel. In certain configurations, theoperation 602 is performed as previously discussed with respect to theshort equalizer section 302. In such configurations, the first equalizedsignal is the signal Y1 408. Similarly, the first estimate of thechannel is H₁ 510 and the first portion of the received signal comprisesthe midamble. The decoding process 600 further comprises the operation604 of producing a second equalized signal using the first equalizedsignal and one of a linear estimator and a non-linear estimator. Incertain configurations, the operation 604 is performed as previouslydiscussed with respect to the channel estimator section 304. In suchconfigurations, the second equalized signal is the output S_(equ) 326.Furthermore, the linear estimator is the combiner section 504 and thenon-linear estimator is the MLSE section 506. The decoding process 600further comprises the operation 606 of estimating a first estimate ofsymbols in the received signal and a second estimate of the channel froma second portion of the received signal. In certain configurations, theoperation 606 is performed as previously discussed with respect to thelong equalizer section 306. The decoding process 600 further comprisesthe operation 608 of generating a second estimate of symbols in thereceived signal based on the second estimate of the channel. In certainconfigurations, the operation 608 is performed as previously discussedwith respect to the interference canceller section 308.

FIG. 7 a is a block diagram illustrating a receiver 700 in accordancewith certain configurations of the present invention. In the illustratedembodiment, symbol decision feedback is used from symbol decisions madein the ICC section 718 to a channel equalizer section 706 tosuccessively improve interference suppression. In certain configuration,the use of feedback to iteratively improve channel suppression lendsitself to an implementation in which a channel equalizer begins aniterative symbol detection process as a “short” equalizer andprogressively becomes a “longer” channel equalizer in successiveiterations. In other words, a channel equalizer section operates as ashort equalizer (on a smaller number of input samples) at the onset ofthe iterative process, and operates as a long equalizer (on a highernumber of input samples compared to the first iteration) in the finaliteration.

As seen in FIG. 7 a, samples of a received signal X₁ 702 and a set ofknown symbols S¹ _(TSC) 704 are input to a channel equalizer section706. In certain configurations, the received signal X₁ 702 is identicalto the received signal X 406, the set of known symbols S¹ _(TSC) 704 isidentical to S_(TSC) 410 of FIG. 4 and the channel equalizer 706 isidentical to the short equalizer 302 of FIG. 3. The channel equalizersection 706 outputs a first equalized signal Y2 708 and a first estimateof the channel. In certain configurations the first equalized signal Y2708 is identical to Y1 408 of FIG. 4. A channel estimator section 710produces a second estimate of the channel H′₁ 716 and a first estimateof symbols. In certain configurations, the channel estimator section 710is identical to the long equalizer section 306 of FIG. 3 and the secondestimate of the channel H′₁ 716 is identical to H₁ 510 of FIG. 5. TheMLSE section 714 receives the first equalized signal Y2 708, after ithas been re-arranged in a spatially decorrelated form in a spatialdecorrelator section 712, to produce a second equalized signal input tothe interference canceller section 718. In certain configurations, theMLSE section 714 is identical to the MLSE section 506 of FIG. 5, and thefirst equalized signal Y2 708 is identical to Y1 408 of FIGS. 4 and 5.The operational principles of a spatial decorrelator section 712 arewell-known in the art.

Still referring to FIG. 7 a, the interference canceller section 718 usesthe first estimate of symbols and a channel estimate from the channelestimator section 710 to generate a second estimate of symbols and alog-likelihood value associated with the second symbol estimates. Incertain configurations, the interference canceller section 718 isidentical to the interference canceller section 308 of FIG. 3. Thechannel estimate may be iteratively refined using a minimum mean squareerrors (MMSE) symbol estimation section 719 that uses a hard slicer anda soft MMSE symbol decision algorithm to produce refined estimates ofsymbols that are further used by the channel equalizer section 706 inthe next iteration. An iteration termination criterion such as meansquare error improvement from one iteration to the next, or expirationof a timing budget to calculate symbol estimate, may be used interminating the iterative estimation process. Previously referenced U.S.patent application Ser. No. 12/553,855 titled “SYMBOL ESTIMATION METHODSAND APPARATUSES” describes certain iterative techniques to refine symbolestimates. A de-interleaver section 720 de-interleaves symbols from thesecond estimate of symbols. In certain configurations, thede-interleaver section 720 is identical to the de-interleaver section310 of FIG. 3. A channel decoder section 722 uses the de-interleavedsymbols to produce data output. In certain configurations, the channeldecoder section 722 is identical to the channel decoder section 312 ofFIG. 3.

FIG. 7 b is a block diagram illustrating a receiver 790 in accordancewith certain other configurations of the present invention. In theillustrated embodiment, symbol decision feedback is used from a symboldecision section to a channel equalizer section to successively improveinterference suppression. In certain configuration, the use of feedbackto iteratively improve channel suppression lends itself to animplementation in which a channel equalizer begins an iterative symboldetection process as a “short” equalizer and progressively becomes a“longer” channel equalizer in successive iterations. In other words, achannel equalizer section operates as a short equalizer (on a smallernumber of input samples) at the onset of the iterative process, andoperates as a long equalizer (on a higher number of input samplescompared to the first iteration) in the final iteration.

As seen in FIG. 7 b, samples of a received signal X₂ 750 and a set ofsymbols S² _(dec) 752 are input to a channel equalizer section 754. Incertain configurations, in the first iteration, the set of symbolsS_(dec) 752 is equal to the set of symbols S¹ _(TSC) 704 of FIG. 7 a.The channel equalizer section 754 outputs a first equalized signal Y3756 and a first estimate of the channel. In certain configurations, thechannel equalizer section 754 is identical to the short equalizersection 302 of FIG. 3 and the first equalized signal Y3 756 is identicalto Y1 408 of FIGS. 4 and 5. A channel estimator section 758 produces asecond estimate of the channel H″₁ 764 and a first estimate of symbols.In certain configurations, the channel estimator section 758 isidentical to the long equalizer section 306 of FIG. 3 and the secondestimate of the channel H″₁ 764 is identical to H₁ 510 of FIG. 5. Acombiner section 762 receives the first equalized signal Y3 756, alignedfor ease of calculations in a stream alignment section 760, to produce asecond equalized signal input to the interference canceller section 766.

Still referring to FIG. 7 b, the stream alignment section 760 operatesto implement the mathematical operations described with respect toequation (9) above. The interference canceller section 766 uses thefirst estimate of symbols and the second estimate of the channel togenerate a second estimate of symbols and a log-likelihood valueassociated with the second symbol estimates. In certain configurations,the combiner section 762 is identical to the combiner section 504 ofFIG. 5 and the interference canceller section 766 is identical to theinterference canceller section 308 of FIG. 3. The channel estimate maybe iteratively refined using a minimum mean square errors (MMSE) symbolestimation section 768 that uses a hard slicer and a soft MMSE symboldecision algorithm to produce refined estimates of symbols that arefurther used by the channel equalizer section 754 in the next iteration.An iteration termination criterion such as mean square error improvementfrom one iteration to the next, or expiration of a timing budget tocalculate symbol estimate, may be used in terminating the iterativeestimation process. Previously referenced U.S. patent application,titled “SYMBOL ESTIMATION METHODS AND APPARATUSES” (Attorney Docket No.091495) describes certain iterative techniques to refine symbolestimates. A de-interleaver section 770 de-interleaves symbols from thesecond estimate of symbols. In certain configurations, thede-interleaver section 770 is identical to the de-interleaver section310 of FIG. 3. A channel decoder section 772 uses the de-interleavedsymbols to produce data output. In certain configurations, the channeldecoder section 772 is identical to the channel decoder section 312 ofFIG. 3.

FIG. 8 is a chart 800 illustrating exemplary performance achievable inaccordance with certain configurations of the subject technology. Chart800 depicts the frame error rate over a range of carrier energy tointerference energy ratios (C/I) for exemplary receiver systemsoperating on GSM TU50 communication channel. As can be seen in chart800, performance using a linear combiner 504 discussed above, shown ascurve 804 (labeled “eSAIC/MEQ”), improves significantly over performancedepicted by curve 802 using a conventional 16-state MLSE channelestimator.

FIG. 9 is a chart 900 illustrating exemplary performance achievable inaccordance with certain configurations of the subject technology. Chart900 depicts the symbol error rate over a range of carrier energy tointerference energy ratios (Eb/No) for exemplary receiver systemsoperating on an EDGE HT100 communication channel, using 8PSK modulationand having CCI. As can be seen in chart 900, the curve 902 representsperformance using certain aspects of the present disclosure (labeled“MEQ/PHIL”) and is seen to improve by over 2 dB compared to performanceusing a conventional 4-state RSSE channel equalization techniquedepicted by curve 904.

FIG. 10 is a block diagram that illustrates exemplary apparatus 1000 inaccordance with certain configurations of the present disclosure. Thereceiver apparatus 1000 comprises means 1002 for producing a firstequalized signal and a first estimate of a channel by operating on afirst portion of a received signal received over a channel, means 1004for producing a second equalized signal using the first equalized signaland one of a linear estimator and a non-linear estimator, means 1006 forestimating a first estimate of symbols in the received signal and asecond estimate of channel from a second portion of the received signaland means 1008 for generating a second estimate of symbols in thereceived signal, based on the second estimate of the channel. Asdepicted in FIG. 10, means 1002, 1004, 1006 and 1008 are incommunication with each other via a communication means 1010.

FIG. 11 is a block diagram that illustrates exemplary receiver system1100 in accordance with certain configurations of the subjecttechnology. The receiver system 1100 comprises a short equalizer section1102 configured to produce a first equalized signal and a first estimateof a channel by operating on a first portion of a received signalreceived over a channel, a channel estimator section 1104 configured toproduce a second equalized signal using the first equalized signal andone of a linear estimator and a non-linear estimator, a long equalizersection 1106 configured to estimate a first estimate of symbols in thereceived signal and a second estimate of channel from a second portionof the received signal and an interference canceller section 1108configured to generate a second estimate of symbols in the receivedsignal, based on the second estimate of the channel. As depicted in FIG.11, the modules 1102, 1104, 1106 and 1108 are in communication via acommunication module 1110.

FIG. 12 is a block diagram that illustrates a computer system 1200 uponwhich an aspect may be implemented. Computer system 1200 includes a bus1202 or other communication mechanism for communicating information, anda processor 1204 coupled with bus 1202 for processing information.Computer system 1200 also includes a memory 1206, such as a randomaccess memory (“RAM”) or other dynamic storage device, coupled to bus1202 for storing information and instructions to be executed byprocessor 1204. Memory 1206 can also be used for storing temporaryvariable or other intermediate information during execution ofinstructions to be executed by processor 1204. Computer system 1200further includes a data storage device 1210, such as a magnetic disk oroptical disk, coupled to bus 1202 for storing information andinstructions.

Computer system 1200 may be coupled via I/O module 1208 to a displaydevice (not illustrated), such as a cathode ray tube (“CRT”) or liquidcrystal display (“LCD”) for displaying information to a computer user.An input device, such as, for example, a keyboard or a mouse may also becoupled to computer system 1200 via I/O module 1208 for communicatinginformation and command selections to processor 1204.

According to one aspect, interference suppression is performed by acomputer system 1200 in response to processor 1204 executing one or moresequences of one or more instructions contained in memory 1206. Suchinstructions may be read into memory 1206 from another machine-readablemedium, such as data storage device 1210. Execution of the sequences ofinstructions contained in main memory 1206 causes processor 1204 toperform the process steps described herein. One or more processors in amulti-processing arrangement may also be employed to execute thesequences of instructions contained in memory 1206. In alternativeaspects, hard-wired circuitry may be used in place of or in combinationwith software instructions to implement various aspects. Thus, aspectsare not limited to any specific combination of hardware circuitry andsoftware.

The term “machine-readable medium” as used herein refers to any mediumthat participates in providing instructions to processor 1204 forexecution. Such a medium may take many forms, including, but not limitedto, non-volatile media, volatile media, and transmission media.Non-volatile media include, for example, optical or magnetic disks, suchas data storage device 1210. Volatile media include dynamic memory, suchas memory 1206. Transmission media include coaxial cables, copper wire,and fiber optics, including the wires that comprise bus 1202.Transmission media can also take the form of acoustic or light waves,such as those generated during radio frequency and infrared datacommunications. Common forms of machine-readable media include, forexample, floppy disk, a flexible disk, hard disk, magnetic tape, anyother magnetic medium, a CD-ROM, DVD, any other optical medium, punchcards, paper tape, any other physical medium with patterns of holes, aRAM, a PROM, an EPROM, a FLASH EPROM, any other memory chip orcartridge, a carrier wave, or any other medium from which a computer canread.

Those of skill in the art would appreciate that the various illustrativeblocks, modules, elements, components, methods, and algorithms describedherein may be implemented as electronic hardware, computer software, orcombinations of both. Furthermore, these may be partitioned differentlythan what is described. To illustrate this interchangeability ofhardware and software, various illustrative sections, blocks, modules,elements, components, methods, and algorithms have been described abovegenerally in terms of their functionality. Whether such functionality isimplemented as hardware or software depends upon the particularapplication and design constraints imposed on the overall system.Skilled artisans may implement the described functionality in varyingways for each particular application.

It is understood that the specific order or hierarchy of steps or blocksin the processes disclosed is an illustration of exemplary approaches.Based upon design preferences, it is understood that the specific orderor hierarchy of steps or blocks in the processes may be rearranged. Theaccompanying method claims present elements of the various steps in asample order, and are not meant to be limited to the specific order orhierarchy presented.

The previous description is provided to enable any person skilled in theart to practice the various aspects described herein. Variousmodifications to these aspects will be readily apparent to those skilledin the art, and the generic principles defined herein may be applied toother aspects. Thus, the claims are not intended to be limited to theaspects shown herein, but is to be accorded the full scope consistentwith the language claims, wherein reference to an element in thesingular is not intended to mean “one and only one” unless specificallyso stated, but rather “one or more.” Unless specifically statedotherwise, the term “some” refers to one or more. Pronouns in themasculine (e.g., his) include the feminine and neuter gender (e.g., herand its) and vice versa. All structural and functional equivalents tothe elements of the various aspects described throughout this disclosurethat are known or later come to be known to those of ordinary skill inthe art are expressly incorporated herein by reference and are intendedto be encompassed by the claims. Moreover, nothing disclosed herein isintended to be dedicated to the public regardless of whether suchdisclosure is explicitly recited in the claims. No claim element is tobe construed under the provisions of 35 U.S.C. §112, sixth paragraph,unless the element is expressly recited using the phrase “means for” or,in the case of a method claim, the element is recited using the phrase“operation for.”

What is claimed is:
 1. A communication receiver comprising: a shortequalizer section configured to operate on a first portion of a receivedsignal received over a channel to produce a first equalized signal and afirst estimate of the channel; a channel estimator section configured tooperate on the first equalized signal to produce a second equalizedsignal, the channel estimator section comprising a linear estimator anda non-linear estimator; a long equalizer section configured to operateon a second portion of the received signal to produce a first estimateof symbols in the received signal and a second estimate of the channel;an interference canceller section configured to operate on the firstestimate of symbols in the received signal to generate a second estimateof symbols in the received signal based on, at least in part, the secondestimate of the channel; an optimal timing section configured to extracttiming information from the received signal; and an optimal frequencysection configured to generate an estimate of a carrier frequency fromthe received signal.
 2. The communication receiver of claim 1, whereinthe channel estimator section further comprises a stream alignmentsection configured to align samples of the first equalized signals forprocessing by the linear estimator.
 3. The communication receiver ofclaim 1, further comprising: a de-interleaver section configured tode-interleave symbols from the second estimate of symbols to produce asymbol sequence, and a channel decoder section configured to generatereceived data from the symbol sequence.
 4. The communication receiver ofclaim 1, wherein the channel estimator is further configured to use oneof the linear estimator or the non-linear estimator in response to amodulation type of the received signal.
 5. The communication receiver ofclaim 4, wherein the channel estimator does not use the non-linearestimator if the modulation type of the received signal comprises morethan one bit per symbol.
 6. The communication receiver of claim 1,wherein the first portion of the received signal comprises a knownsignal.
 7. The communication receiver of claim 6, wherein the knownsignal comprises a midamble.
 8. The communication receiver of claim 1,wherein the second equalized signal comprises a midamble portion and adata burst portion.
 9. The communication receiver of claim 1, whereinthe short equalizer section is further configured to use the estimate ofthe carrier frequency and the timing information to minimize anestimation error incurred in producing the first equalized signal andthe first estimate of the channel.
 10. The communication receiver ofclaim 1, wherein the short equalizer section is further configured toproduce the first equalized signal using a blind estimation algorithm.11. The communication receiver of claim 1, wherein the linear estimatoris configured to produce the second equalized signal by weighing symbolsin the first equalized signal by a measure of energy in the firstestimate of the channel.
 12. The communication receiver of claim 1,further comprising a minimum mean squared error (MMSE) symbol estimationsection configured to provide symbol estimates to the short equalizersection and wherein the channel estimator section is configured toproduce the second equalized signal using the linear estimator.
 13. Asignal reception method comprising: producing a first equalized signaland a first estimate of a channel by operating on a first portion of areceived signal received over the channel; producing a second equalizedsignal using the first equalized signal and one of a linear estimatorand a non-linear estimator; estimating a first estimate of symbols inthe received signal and a second estimate of the channel from a secondportion of the received signal; generating a second estimate of symbolsin the received signal based on the second estimate of the channel;extracting timing information from the received signal; and generatingan estimate of a carrier frequency from the received signal.
 14. Thesignal reception method of claim 13, further comprising: aligningsamples of the first equalized signals for processing by the linearestimator.
 15. The signal reception method of claim 13, furthercomprising: de-interleaving symbols from the second estimate of symbolsto produce a symbol sequence, and generating received data from thesymbol sequence.
 16. The signal reception method of claim 13, whereinthe operation of producing the second equalized signal furthercomprises: selectively using one of the linear estimator or thenon-linear estimator in response to a modulation type of the receivedsignal.
 17. The signal reception method of claim 13, wherein theoperation of producing the second equalized signal does not use thenon-linear estimator when the modulation type of the received signalcomprises more than one bit per symbol.
 18. The signal reception methodof claim 13, wherein the first portion of the received signal comprisesa known signal.
 19. The signal reception method of claim 18, wherein theknown signal comprises a midamble.
 20. The signal reception method ofclaim 13, wherein the second equalized signal comprises a midambleportion and a data burst portion.
 21. The signal reception method ofclaim 13, wherein the operation of producing the first equalized signalfurther comprises using the estimate of the carrier frequency and thetiming information to minimize an estimation error incurred in producingthe first equalized signal and the first estimate of the channel. 22.The signal reception method of claim 13, wherein the operation ofproducing the first equalized signal further comprises producing thefirst equalized signal using a blind estimation algorithm.
 23. Thesignal reception method of claim 13, wherein the operation of producingthe second equalized signal further comprises producing the secondequalized signal by weighing symbols in the first equalized signal by ameasure of energy in the first estimate of the channel.
 24. The signalreception method of claim 13, further comprising: iteratively using,until an iteration termination criterion is met, the second estimate ofsymbols in the operation of producing the first equalized channel byincreasing a number of samples in the first portion of the receivedsignal in each successive iteration and wherein the operation ofproducing the second equalized signal is performed using the linearestimator.
 25. A non-transitory machine-readable medium comprisinginstructions for receiving a signal at a receiver, the instructionscomprising: code for producing a first equalized signal and a firstestimate of a channel by operating on a first portion of a receivedsignal received over the channel; code for producing a second equalizedsignal using the first equalized signal and one of a linear estimatorand a non-linear estimator; code for estimating a first estimate ofsymbols in the received signal and a second estimate of the channel froma second portion of the received signal; code for generating a secondestimate of symbols in the received signal based on the second estimateof the channel; code for extracting timing information from the receivedsignal; and code for generating an estimate of a carrier frequency fromthe received signal.
 26. The non-transitory machine-readable medium ofclaim 25, wherein the instructions further comprise: code for aligningsamples of the first equalized signals for processing by the linearestimator.
 27. The non-transitory machine-readable medium of claim 25,wherein the instructions further comprise: code for de-interleavingsymbols from the second estimate of symbols to produce a symbolsequence, and code for generating received data from the symbolsequence.
 28. The non-transitory machine-readable medium of claim 25,wherein the code for producing the second equalized signal furthercomprises: code for selectively using one of the linear estimator or thenon-linear estimator in response to a modulation type of the receivedsignal.
 29. The non-transitory machine-readable medium of claim 25,wherein the code for producing the second equalized signal does notdisable the use of the non-linear estimator if the modulation type ofthe received signal comprises more than one bit per symbol.
 30. Thenon-transitory machine-readable medium of claim 25, wherein the firstportion of the received signal comprises a known signal.
 31. Thenon-transitory machine-readable medium of claim 30, wherein the knownsignal comprises a midamble.
 32. The non-transitory machine-readablemedium of claim 25, wherein the second equalized signal comprises amidamble portion and a data burst portion.
 33. The non-transitorymachine-readable medium of claim 25, wherein the code for producing thefirst equalized signal further comprises code for using the estimate ofthe carrier frequency and the timing information to minimize anestimation error incurred in producing the first equalized signal andthe first estimate of the channel.
 34. The non-transitorymachine-readable medium of claim 25, wherein the code for producing thefirst equalized signal further comprises code for producing the firstequalized signal using a blind estimation algorithm.
 35. Thenon-transitory machine-readable medium of claim 25, wherein the code forproducing the second equalized signal further comprises code forproducing the second equalized signal by weighing symbols in the firstequalized signal by a measure of energy in the first estimate of thechannel.
 36. The non-transitory machine-readable medium of claim 25,wherein the instructions further comprise: code for iteratively using,until an iteration termination criterion is met, the second estimate ofsymbols in the operation of producing the first equalized channel byincreasing a number of samples in the first portion of the receivedsignal in each successive iteration and wherein the operation ofproducing the second equalized signal is performed using the linearestimator.
 37. A signal reception apparatus comprising: means forproducing a first equalized signal and a first estimate of a channel byoperating on a first portion of a received signal received over thechannel; means for producing a second equalized signal using the firstequalized signal and one of a linear estimator and a non-linearestimator; means for estimating a first estimate of symbols in thereceived signal and a second estimate of the channel from a secondportion of the received signal; means for generating a second estimateof symbols in the received signal based on the second estimate of thechannel; means for extracting timing information from the receivedsignal; and means for generating an estimate of a carrier frequency fromthe received signal.
 38. The signal reception apparatus of claim 37,further comprising: means for aligning samples of the first equalizedsignals for processing by the linear estimator.
 39. The signal receptionapparatus of claim 37, further comprising: means for de-interleavingsymbols from the second estimate of symbols to produce a symbolsequence, and means for generating received data from the symbolsequence.
 40. The signal reception apparatus of claim 37, wherein themeans for producing the second equalized signal further comprises: meansfor selectively using one of the linear estimator or the non-linearestimator in response to a modulation type of the received signal. 41.The signal reception apparatus of claim 37, wherein the means forproducing the second equalized signal does not use the non-linearestimator if the modulation type of the received signal comprises morethan one bit per symbol.
 42. The signal reception apparatus of claim 37,wherein the first portion of the received signal comprises a knownsignal.
 43. The signal reception apparatus of claim 42, wherein theknown signal comprises a midamble.
 44. The signal reception apparatus ofclaim 37, wherein the second equalized signal comprises a midambleportion and a data burst portion.
 45. The signal reception apparatus ofclaim 37, wherein the means for producing the first equalized signalfurther comprises means for using the estimate of the carrier frequencyand the timing information to minimize an estimation error incurred inproducing the first equalized signal and the first estimate of thechannel.
 46. The signal reception apparatus of claim 37, wherein themeans for producing the first equalized signal further comprises meansfor producing the first equalized signal using a blind estimationalgorithm.
 47. The signal reception apparatus of claim 37, wherein themeans for producing the second equalized signal further comprises meansfor producing the second equalized signal by weighing symbols in thefirst equalized signal by a measure of energy in the first estimate ofthe channel.
 48. The signal reception apparatus of claim 37, furthercomprising: means for iteratively using, until an iteration terminationcriterion is met, the second estimate of symbols in the operation ofproducing the first equalized channel by increasing a number of samplesin the first portion of the received signal in each successive iterationand wherein the means for producing the second equalized signalcomprises means for performing equalization using the linear estimator.49. A communication device comprising: a memory; and a processorconfigured to execute instructions to: produce a first equalized signaland a first estimate of a channel by operating on a first portion of areceived signal received over the channel; produce a second equalizedsignal using the first equalized signal and one of a linear estimatorand a non-linear estimator; estimate a first estimate of symbols in thereceived signal and a second estimate of the channel from a secondportion of the received signal; generate a second estimate of symbols inthe received signal based on the second estimate of the channel; extracttiming information from the received signal; and generate an estimate ofa carrier frequency from the received signal.
 50. The communicationdevice of claim 49, wherein the processor is further configured toexecute instructions to: align samples of the first equalized signalsfor processing by the linear estimator.
 51. The communication device ofclaim 49, wherein the processor is further configured to executeinstructions to: de-interleave symbols from the second estimate ofsymbols to produce a symbol sequence, and generate received data fromthe symbol sequence.
 52. The communication device of claim 49, whereinthe processor is further configured to execute instructions to:selectively use one of the linear estimator or the non-linear estimatorin response to a modulation type of the received signal.
 53. Thecommunication device of claim 49, wherein the instructions to producethe second equalized signal do not include instructions to disable theuse of the non-linear estimator if the modulation type of the receivedsignal comprises more than one bit per symbol.
 54. The communicationdevice of claim 49, wherein the first portion of the received signalcomprises a known signal.
 55. The communication device of claim 54,wherein the known signal comprises a midamble.
 56. The communicationdevice of claim 49, wherein the second equalized signal comprises amidamble portion and a data burst portion.
 57. The communication deviceof claim 49, wherein the instructions to produce the first equalizedsignal further comprise instructions to use the estimate of the carrierfrequency and the timing information to minimize an estimation errorincurred in producing the first equalized signal and the first estimateof the channel.
 58. The communication device of claim 49, wherein theinstructions to produce the first equalized signal further compriseinstructions to produce the first equalized signal using a blindestimation algorithm.
 59. The communication device of claim 49, whereinthe instructions to produce the second equalized signal further compriseinstructions to produce the second equalized signal by weighing symbolsin the first equalized signal by a measure of energy in the firstestimate of the channel.
 60. The communication device of claim 49,wherein the processor is further configured to execute instructions to:iteratively use, until an iteration termination criterion is met, thesecond estimate of symbols to produce the first equalized channel byincreasing a number of samples in the first portion of the receivedsignal in each successive iteration and wherein the instructions toproduce the second equalized signal comprise instructions to produce thesecond equalized signal using the linear estimator.